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WMR31110.1177/0734242X12462281Waste Management & ResearchWei et al.
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Short Report
Design, construction and management of tailings storage facilities for surface disposal in China: case studies of failures
Waste Management & Research 31(1) 106–112 © The Author(s) 2013 Reprints and permission: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0734242X12462281 wmr.sagepub.com
Zuoan Wei1,3,4, Guangzhi Yin1,3,4, J G Wang2, Ling Wan1,4 and Guangzhi Li1,4
Abstract Rapid development of China’s economy demands for more mineral resources. At the same time, a vast quantity of mine tailings, as the waste byproduct of mining and mineral processing, is being produced in huge proportions. Tailings impoundments play an important role in the practical surface disposal of these large quantities of mining waste. Historically, tailings were relatively small in quantity and had no commercial value, thus little attention was paid to their disposal. The tailings were preferably discharged near the mines and few tailings storage facilities were constructed in mainland China. This situation has significantly changed since 2000, because the Chinese economy is growing rapidly and Chinese regulations and legislation require that tailings disposal systems must be ready before the mining operation begins. Consequently, data up to 2008 shows that more than 12 000 tailings storage facilities have been built in China. This paper reviews the history of tailings disposal in China, discusses three cases of tailings dam failures and explores failure mechanisms, and the procedures commonly used in China for planning, design, construction and management of tailings impoundments. This paper also discusses the current situation, shortcomings and key weaknesses, as well as future development trends for tailings storage facilities in China. Keywords Tailings disposal, tailings management, tailings dam failures, environmental hazards, China tailings dams
Introduction China is currently one of the world leaders in both exploitation and consumption of mineral resources. Billions of tonnes of metal ores are mined in China every year, and billion of tonnes of tailings and wastes as byproducts are disposed of on the ground. In the early 1980s, tailings were considered as residue with no commercial value. Most of the small and medium-size mines directly discharged their tailings into the local valleys or rivers close to the mines. Consequently the mining industry developed a poor reputation for waste disposal management. With the enhancement of environmental protection awareness, both regulations and legislation were successively promulgated and implemented in the early 1990s, requiring mine owners to build tailings disposal facilities and water treatment systems before any commercial mining may commence. The impoundments are regarded as a major part of the mining facilities and were used to store tailings and waste water from mineral processing (Kanagasbai 1980; Kwak et al., 2005). With the growth of the mining industry in China, many tailings impoundments have been built and more are planned. Up to now, China has achieved success in tailings
disposal and has greatly improved its environmental performance in relation to mining activities. The authors consider that this experience and the lessons learned by China’s mine operators may also be useful to mine operators in other countries. Herein, the history of tailings disposal in China is discussed and three examples of tailings dam failures in China are analysed in detail. The procedures of planning, design and construction of tailings 1 State
Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing, China 2 School of Mechanical and Chemical Engineering, The University of Western Australia, Crawley, Western Australia, Australia 3 State and Local Joint Engineering Laboratory of Methane Drainage in Complex Coal Gas Seam, Chongqing University, Chongqing, China 4 College of Resource and Environmental Science, Chongqing University, Chongqing, China Corresponding author: Zuoan Wei, State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, No. 174 Shapingba Zhengjie, Chongqing, 400030, China. Email:
[email protected]
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Wei et al. impoundments in China are also discussed. Finally the current situation, key weaknesses, and future development trends for tailings storage facilities in China are presented.
History of tailings disposal From 1949 to the present day, the history of tailings disposal in China can be divided into the following four major phases. Prior to 1958, mainland China had a few mines and the production of minerals by milling was relatively small in quantity. For example, the steel production in 1949 was only about 158 000 tonnes per year. Such a low production only required a small amount of mine resources and thus the disposal of the tailings was not considered as a problem. Between 1958 and 1978, the national mining industry started a phase of new development and growth. In 1958, the Chinese government launched a campaign of increased steel-making, requesting that steel and iron production achieved 10 700 000 tonnes per year. At that time only a few ore mines, such as Hainan iron ore mine, Anshan iron ore mine, and Yunnan tin mine were either planned or operating in the whole country. These were small and medium-sized state-owned mines. During this period, mineral processing technology was poorly developed and the production of mineral milling was relatively small. Only some medium-size mines built specific tailings storage facilities. Most of the mines had no tailings disposal facilities due to poor environmental protection awareness. Their tailings were directly discharged into valleys or rivers near the mines. This situation did not change much until the late 1980s. From 1978 to 2000, the number of tailings disposal facilities steadily increased, and the mine environment slowly changed. The Chinese government promulgated the first Environmental Protection Law in 1989 and relevant regulations in 1996, respectively. According to these legislative codes, all mines must construct tailings ponds otherwise the mine may be closed by local government. Since then the quantity of tailings ponds has dramatically increased, reaching more than 6000 by the year 2000. The planning, construction and operation of tailings storage facilities has become an increasingly important issue for miners. From 2000 to the present, the mining industry has developed rapidly along with the rapid economic development within China. The quantities of tailings discharged from mines also increased considerably. Data show that there were more than 12 000
tailings ponds up to 2008 (Yin et al., 2011). With the increase of the number of tailings ponds, some disastrous failures of tailings dams have occasionally occurred. Consequently the issue of safety of tailings ponds has become an increasing concern for both local residents and governments.
Three examples of failure of tailing dams in China In conjunction with increased mineral production a number of tailings dam failures have occurred in China since 1960. These failures have had significantly adverse socioeconomic consequences, resulting in the loss of many lives, property damage and serious pollution problems in downstream areas. The earliest documented failure of a tailings dam took place in Yunnan province in 1962. At that time, people did not fully appreciate the consequences of tailings dam failures. Communications across the country were also weak and sharing of information on failures was relatively poor. Many small tailings dam failures were neither recorded nor reported. Table 1 summarizes the main failures of tailings dams that have occurred in China. From these limited records, three typical cases are analysed below.
Huogudu tin tailings pond, Yunnan province Huogudu tailings pond was owned by the Yunnan Tin Company and located near Gejiu, a city in Yunnan province. This tailings pond was designed in June 1956, constructed in July 1957, and commissioned in August 1958. The pond was in a valley and the tailings dam was built by the upstream method. At approximately 0230 to 0300 h on 26 September 1962, the main tailings dam ruptured after 3 days of moderate rainfall (see Figure 1). The breach width was about 113 m on the top and 45 m at the bottom and its depth was about 14 m. At the time of failure, the pond stored about 5.42 × 106 m3 tailings and the tailings dam reached 19.0 m in height and 441.0 m in length. The failure released approximately 3.30 × 106 m3 of tailings and 3.8 × 105 m3 of water into downstream areas. The tailings flowed as far as 4.5 km from the dam site. The tailings and water destroyed 11 villages, causing 171 deaths and 92 injuries, and rendered 13 970 persons homeless. After the event, a forensic analysis was carried out by a specialist team of professionals. The analysis revealed that the intense
Table 1. Main failures of tailings dams in China. Name of dam
Type of tailings
Method of construction
Year of failure Consequences of failure
Huogudu, Yunnan Tin Group Co., Yunnan Niujiaolong, Shizhuyuan Non-ferrous Metals Co., Hunan Longjiaoshan, Daye Iron Ore mine, Hubei Dachang, Nandan Tin mine, Guangxi Zhenan Gold mine, Shanxi Xiangfen tailings pond, Shanxi province
Tin Copper
Upstream Upstream
1962 1985
171 killed 49 killed
Iron Tin Gold Iron
Upstream Upstream Upstream Upstream
1994 2000 2006 2008
31 killed 28 killed 17 killed 277 killed
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Figure 1. Plan view of Huogudu tailings pond.
Figure 2. Plan view of Niujiaolong tailings pond.
rainfall was the direct cause of the failure, and the lack of experience in pond management was identified as an indirect cause.
Niujiaolong tailings pond, Hunan province Niujiaolong tailings pond was owned by Shizhuyuan Zinc Mine Company and located in a valley near the mine site. The tailings dam was constructed by the upstream method. The system of tailings ponds was commissioned in 1971 and the design operational lifetime was 13 years. At that time the design height was 57 m, and the design capacity was 2.15 × 106 m3. A typhoon caused heavy rainstorms at the mine from 22 to 24 August 1985. In the early morning of 25 August the strong rainstorms triggered some flash flooding and mud-debris flows around the mine area. The debris flowed down the mountain and entered into the Niujiaolong tailings pond from locations 1# to 5#, as shown in Figure 2. The debris flows forced the pond water to overtop the tailings dam resulting in failure. At the time of failure the tailings pond stored about 1.1 × 106 m3 tailings to a height of 40 m. This failure released approximately 7.3 × 105 m3
tailings. The tailings flowed as far as 4.2 km from the dam site, destroyed many houses, caused 49 deaths, and resulted in about US$ 1.6 × 106 in direct losses. The failure also resulted in significant pollution of the affected area. The cause of failure was mainly attributed to meteorological conditions.
Xiangfen tailings pond, Shanxi province Xiangfen tailings pond was built in a valley near an iron ore mine in 1977. At that time, the iron ore mine was owned by a large state-owned steel company. With the mining industry downturn in the 1980s, the mine was shut down and tailings deposition was suspended. In 2005, this mine was reopened by a local private company. In September 2007, the tailings pond was illegally reused by this company. Due to lack of proper tailings pond management, the tailings pond was simultaneously used for tailings depositions and as a water reservoir for the concentrator mill. The pond was also used to hold extracted groundwater. At 0758 h on 8 September 2008 the tailings dam failed. At that time, the tailings pond held about 2.9 × 105 m3 tailings
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Wei et al. and the dam was 50.7 m high. This failure released approximately 1.9 × 105 m3 tailings. The tailings flowed as far as 2.5 km downstream and covered about 35 hectares of land. Figure 3 shows a photograph at the failure and a sketch of the extent of the tailings slurry. The tailings destroyed many houses, caused 277 deaths, 33 injuries, and caused about US$ 1.3 × 107 in direct losses. The failure also resulted in very serious social impacts. The failure was mainly attributed to poor impoundment management. First, in order to store more tailings, the slope of the dam wall was built to a vertical (V): horizontal (H) ratio of V 1 : H 1.4 (see Figure 4(a) and (b)) after the pond was illegally reused, which is significantly steeper than the V 1 : H 4.0 to V 1 : H 5.0 as required by the applicable technical standards. Second, this tailings pond was incorrectly used as a water reservoir to store water for the concentrator mill with the supernatant pond kept at a high level. This combination produced a relatively short tailings bench and a high phreatic surface (Figure 4(b)) and resulted in significant seepage through the dam wall. Finally, a loess wall 4.0 m wide was built on the tailings dam wall (see Figure 4 (c)) in an attempt to solve seepage and slope stability problems. The fine loess material reduced seepage but this resulted in the saturation zone inside the dam continually extending with the rising water level, with a corresponding reduction in dam stability. The tailings dam eventually failed under these worsening conditions (see Figure 4(d)). This failure was therefore due to human factors.
Figure 3. Failure of Xiangfen tailings dam: (a) picture of the tailings pond after failure; (b) sketch plan of the tailings slurry flowing downstream.
Cause analysis of tailings dam failures In China, over 95% of tailings pond incidents occurred in operations. Tailings dam failures rarely occurred in abandoned or inactive tailings ponds. Accidents were normally triggered by either natural or human factors. Investigations show that the most common cause of tailings dam failure is related to heavy rainfall or snowmelt events. Engineering design did not have a demonstrated capability to cope with extreme-event climatic conditions because of a lack of climatic data. This is despite a flood capacity assessment being undertaken during design. Consequently, the ponds did not have enough volume to store the flood water from the surrounding areas and tailings dam failures occurred. The second important cause is related to human factors, such as poor design and construction of initial dyke and drainage culverts, or poor management and inadequate maintenance activities at the tailings dam sites. For example, the cause of failure of the Shuanghe vanadium mine tailings pond in Shanxi province in 2008 was due to failure of the drainage culvert under the tailings dam. This accident caused 3000 m3 tailings and waste water to flow into downstream rivers. Illegal and extended use of tailings ponds by some private miners are also a common human cause for failures. Table 2 summarizes the proportional distributions of the causes of tailings dam failures.
Procedure of design and construction of tailings ponds Prior to 1990, China was relatively lacking in technical standards and guidelines for tailings storage facilities. Design, construction, and subsequent operational management of tailings ponds were essentially carried out according to conventional water storage specifications and experiences. In 1990, the first specific design standard for tailings disposal, termed the Code for Design of Tailings Disposal Facilities of Concentration Plant (ZBJ1-90), was promulgated and implementation began in January 1991. Since then, the design level of tailings ponds has been greatly improved with the increasing number of tailings ponds built. By March of 2006, a standard for safety management of tailings ponds, termed the Safety Technical Regulations for the Tailings Pond (AQ 2006-2005), was promulgated and implemented. These safety regulations provide guidance to mine owners on how to safely and environmentally manage tailings facilities. Currently mine owners select professional design firms for tailings dam design to ensure project success. The design procedure is divided into the three main steps listed here, based on the ZBJ1-90. 1. Collect data and information. The information mainly comprises the capacity per year of the concentration plant, ore type, processing type, tailings characteristics, local meteorological and hydrological data for the mine, and so on. 2. Determine the site of tailings pond. Several possible sites are chosen based on a topographic map of the mine area. Then each possible site is evaluated based on field investigations,
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Waste Management & Research 31(1) At this step, two most important calculations have to be carried out according to the ZBJ1-90: the stability analysis of the tailings dam, in which the limit equilibrium method is recommended, and the flood control capacity analysis (maximum probable flood) of tailings pond and drainage system. Once all the construction drawings of the tailings pond have been completed, tenders or bids are requested from the mine owner to select a construction company for the project construction. The construction project typically includes the starter dyke, transportation system of the tailings slurry from the mill to the pond, the drainage system of the pond and other facilities. Once the construction project is completed and officially credited, the project is handed over to the mine owner. The project starts the operation and the mine owner takes responsibility for the project management and operation. Based on Chinese laws, the design firm and the construction company must have their professional licences and certificates for design and construction of tailings storage facilities. Otherwise, these facilities are illegal and companies may be prosecuted under law.
Current situation and further development in China Characteristics of tailings ponds At the end of 2008, there were 12 655 tailings ponds in China. Their distribution is summarized in Table 3, and their characteristics are summarized in the following list. Figure 4. Construction procedure of tailings dam and failure model: (a) the section of the tailings dam not reused until 2005; (b) the section of the tailings dam after reuse in 2007; (c) the section of the tailings dam before the failure; (d) the failure caused sliding. Table 2. Statistical distribution of tailings dam failure causes in China. Main causes of dam failure
Rate (%)
Start dyke seepage Raised dyke break Slope seepage Drainage facilities damage Flood overtopping/overflow Dam slope instability Landslide around tailings pond Seismic liquefaction
5.1 9.0 14.1 28.2 25.6 1.3 14.1 2.6
analysis and calculations. Their advantages and disadvantages are assessed to determine the most suitable site. 3. Produce drawings and documents describing the tailings disposal facility. After the site of the tailings pond is determined, the primary design document is formed by the design firm according to related national standards. The primary design is then examined officially by a specialist group organized by the local government and detailed construction drawings are created by the design firm.
1. The quantity of tailings ponds is very large and widely distributed across China. Only a few provinces such as Shanghai and Tianjin do not have tailings ponds. About 200 additional tailings ponds are constructed each year (Yin et al., 2004). 2. Most tailings ponds are small in size. Among all the tailings ponds, 12 122 tailings ponds are classified as small, accounting for 95.8% of the total volume. In this context small represents less than 60 m in dam height. Furthermore, over 60% of the tailings dams are less than 10-30 m in height. Most of these small tailings ponds belong to private miners. 3. Ninety-five percent of the tailings dams were constructed by the upstream method, the simplest and most economical construction method that is generally available. Unfortunately, these tailings dams are also inherently weaker and less stable than those dams constructed using other methods.
Main issues for safety enhancement Although great advances have been made in the safety management of tailings ponds, the following issues in design, construction and management of tailings ponds still require improvement. 1. Outdated technology and poor management. The upstream method is the oldest construction method and still the main
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Wei et al. Table 3. Distribution of tailings ponds in mainland China (in 2008). No.
Province
Total tailings ponds
Active
Inactive
Closed
Constructing
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Jiangsu Beijing Qinghai Heilongjiang Zhejiang Xinjiang Sichuan Jilin Gansu Guizhou Guangdong Hubei Fujian Shanxi Anhui Jiangxi Shandong Guangxi Hunan Henan Inner Mongolia Yunnan Liaoning Shanxi Hebei
19 37 57 62 78 103 137 167 183 219 226 236 247 269 341 380 494 504 651 681 685 692 1475 1735 2888
13 9 10 45 44 47 87 112 107 103 63 54 136 125 263 234 252 184 356 275 449 457 1091 602 1773
0 0 44 3 8 0 6 2 24 36 101 149 0 25 6 45 25 136 109 281 118 54 90 247 343
5 28 1 0 25 11 7 22 8 50 47 3 36 49 27 26 136 116 160 5 14 104 120 330 614
1 0 2 14 1 45 37 31 44 30 15 30 75 70 45 75 81 68 26 120 104 77 174 556 158
method for tailings dam construction in China. The only design technical standard of tailings disposal (ZBJ 1-90) has not been revised since it was implemented in 1990. Most of the operators at the site are unskilled workers and most mines are lacking professional advice or good tailings pond management. These situations frequently lead to accidents. 2. The equipment and technology for the safety monitoring of tailings pond are of low standard and lag behind the current development of the mining industry. Up to now, most tailings dam safety management is based on experience due to lack of effective monitoring tools. In some mines, monitoring facilities were not of sufficient accuracy to act as an effective alarm. 3. Backfilling of underground mines is limited necessitating storage of large volumes of tailings ponds and dams.
1. Strengthen the application of research and technical innovation. It is suggested that the centerline construction method be considered for use. Some new methods such as the reinforced terraced fields method (RTFM) (Wei et al., 2006; 2008) can be also used. Furthermore, the government and related agencies should carry out new research on engineered tailings disposal, such as thickened discharge, paste fill, filtered tailings and dry stacking. This may result in new deposition methods and eliminate the need for tailings ponds. 2. Enhance safety management. The emphasis should be put on pre-failure prevention rather than post-failure repair (Rico et al., 2008a; 2008b). 3. Reutilization of tailings. For example, tailings can be reused to produce building materials. This also prolongs the life of storage facilities.
Future development
Conclusions and recommendation
Statistically tailings ponds are one of the main sources of risk for the mining industry. The safe management of tailings facilities is of increasing concern for both local governments and local communities. Consequently technical standards for design, construction and management of tailings ponds require urgent revision. The government and the national societies of mines should increase investment to support application research and technical innovation in line with the rate of increase in mining. At present, the following main development trends are envisaged.
Currently China has more than 12 000 tailings ponds, 95% of which use the upstream method to construct their tailings dam. The small size tailings ponds account for 95.8%, and most of these belong to private miners. Whereas the design and construction of tailings storage facilities are in accordance with Chinese regulations the level of operational management is lower in comparison with developed countries. This results in most of the tailings ponds having one or more deficiencies. Monitoring technology for tailings dam is also relatively poor. Although
112 assessment of flood capacity of the tailings impoundment is undertaken during design, floods due to extreme climatic conditions remain a direct cause of tailings dam failures. Another direct cause of tailings dam failures is the low level of operation management and lack of professional advice. The future development trend is to carry out new engineering research and innovation for tailings disposal, such as thickened discharge, paste fill, filtered tailings and dry stack, as well as increased reutilization of tailings.
Acknowledgements The authors are very grateful to Dr Allen L. Li (URS Australia Pty Ltd., Australia) and Dr Shen Jiayi and anonymous reviewers for their very useful comments and reviews.
Funding This research has been funded by the National Natural Science Foundation of China (No. 51074199).
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